Vilhuer

Friend is building engine for Rotrex SC. Reasoning behind using 951 was that they are build for boost. Piston tops are better suited for high temps and possibly piston diameter is more cone shaped that in NA pistons allowing more heat expansion.

Idea of having top 2mm of cylinder bore exposed when mixture is ignited don't sound very wise to me. What happens to then walls if there is even small problems in timing or engine knocks?

Jfrahm

944NA pistons have a weird round dish offset from the center. 944 Turbo pistons have a big bathtub.

NA piston:
http://www.msprotege.com/members/Bri...20-%20(51).jpg

944 turbo pistons:
http://www.clarks-garage.com/graphics/piston2.jpg

gruffalo

Well, I might be in well over my head here. If no-one has done this before, I'm sure I'm not the right one to try it out first.

Will MSDS headers work well on an Euro S btw?

Fabio421

I am glad you have posted this thread. I have long wondered if it would be possible to build a 5L with the 16v euro heads, cams and intake while using 951 pistons. Then boosting it with confidence. The low C/R isn't that big of a problem since your boosting. I have heard that you may need to use modified rods if you do this. It may be that the builder was trying to gain C/R by using slightly longer rods. I will try to find the thread. Maybe someone can comment on this.

gruffalo

I'm thinking N/A, and for that I'll be aiming for around 10:1 CR. That's the issue here, to somehow get a reasonable CR for N/A with a euro 16v top end on an S4 block.

Fabio421

Since you are looking for that I will help. In the spirit of cooperation I will be glad to trade you my rare (in Norway) US top end for your Euro stuff.

mark kibort

cool shots. so, what is the ccs of the 944 NA head combustion chamber? must be smaller than the euro S heads.

if so, are the 944 heads a way to increase the combustion of the euro 4.7 motors? are they also the same sized valves as the euro . (ie 45mm intake)

MK

FlyingDog

Isn't that half the fun?

hacker-pschorr

There is a 928S4 with turbo pistons up here. The reason for 951 pistons was to lower the compression ratio and be stronger for boosting.

I have no idea where the CR ended up since they were also combined with custom connecting rods.

Vilhuer

I think 944 NA pic shows US model pistons. ROW 944 has higher compression ratio IIRR and piston top has smaller cc.

I think they are somewhat different than 16V 928 heads. Exactly what cc they would result would need to be checked. 11-12 maybe.

Ian928

Wow, that's a big dish! This makes me wonder, as I recall, someone on this list did modify 944 heads to fit a 928. If the 944 heads are that different, what compression did they end up with?

gruffalo

Mark, the 5L block and pistons used in your picture, are they from an 85/86 early 5L or S4?

I wanna know if your drawing/cuts will apply for an S4 block.

SwayBar

It's around 7.5:1.

No; I'm pretty sure he used stock S4 rods.

FlyingDog

US 85-86 pistons and S2 heads should give you a little under 10:1. The numbers have been posted here before.

mark kibort

the pistons are from an 85-86 US. you can tell by the little dish in the middle of the piston. on an S4 it is very large, and hence the reason you can use the S4 pistons for a hybrid motor. this means the heads on an S4 have a lot less CCs. so, an interesting rebuild would be using an 85 block with S4 heads to bump the compression to 12:1. plus you get the larger valves of the S4 heads and by using the 85 cams (same as GT) you get the best performance package of the stock components. I dont think anyone has ever done this yet.

Mk